WorldWideWeb.docx

WorldWideWeb.docx

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WorldWideWeb

World-Wide-Web

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ScholarsgenerallyagreethataturningpointfortheWorldWideWebbeganwiththeintroductionoftheMosaicWebbrowserin1993,agraphicalbrowserdevelopedbyateamattheNationalCenterforSupercomputingApplicationsattheUniversityofIllinoisatUrbana-Champaign（NCSA-UIUC）,ledbyMarcAndreessen.FundingforMosaiccamefromtheU.S.High-PerformanceComputingandCommunicationsInitiative,afundingprograminitiatedbytheHighPerformanceComputingandCommunicationActof1991,oneofseveralcomputingdevelopmentsinitiatedbyU.S.SenatorAlGore.PriortothereleaseofMosaic,graphicswerenotcommonlymixedwithtextinWebpages,anditspopularitywaslessthanolderprotocolsinuseovertheInternet,suchasGopherandWideAreaInformationServers（WAIS）.Mosaic'sgraphicaluserinterfaceallowedtheWebtobecome,byfar,themostpopularInternetprotocol.

TheWorldWideWebConsortium（W3C）wasfoundedbyTimBerners-LeeafterhelefttheEuropeanOrganizationforNuclearResearch（CERN）inOctober,1994.ItwasfoundedattheMassachusettsInstituteofTechnologyLaboratoryforComputerScience（MIT/LCS）withsupportfromtheDefenseAdvancedResearchProjectsAgency（DARPA）—whichhadpioneeredtheInternet—andtheEuropeanCommission.

Bytheendof1994,whilethetotalnumberofwebsiteswasstillminutecomparedtopresentstandards,quiteanumberofnotablewebsiteswerealreadyactive,manyofwhomaretheprecursorsorinspiringexamplesoftoday'smostpopularservices.

Howitworks

ThetermsInternetandWorldWideWebareoftenusedinevery-dayspeechwithoutmuchdistinction.However,theInternetandtheWorldWideWebarenotoneandthesame.TheInternetisaglobaldatacommunicationssystem.Itisahardwareandsoftwareinfrastructurethatprovidesconnectivitybetweencomputers.Incontrast,theWebisoneoftheservicescommunicatedviatheInternet.Itisacollectionofinterconnecteddocumentsandotherresources,linkedbyhyperlinksandURLs.Inshort,theWebisanapplicationrunningontheInternet.

ViewingaWebpageontheWorldWideWebnormallybeginseitherbytypingtheURLofthepageintoaWebbrowser,orbyfollowingahyperlinktothatpageorresource.TheWebbrowsertheninitiatesaseriesofcommunicationmessages,behindthescenes,inordertofetchanddisplayit.

First,theserver-nameportionoftheURLisresolvedintoanIPaddressusingtheglobal,distributedInternetdatabaseknownasthedomainnamesystem,orDNS.ThisIPaddressisnecessarytocontacttheWebserver.ThebrowserthenrequeststheresourcebysendinganHTTPrequesttotheWebserveratthatparticularaddress.InthecaseofatypicalWebpage,theHTMLtextofthepageisrequestedfirstandparsedimmediatelybytheWebbrowser,whichthenmakesadditionalrequestsforimagesandanyotherfilesthatformpartsofthepage.Statisticsmeasuringawebsite'spopularityareusuallybasedeitheronthenumberof'pageviews'orassociatedserver'hits'（filerequests）thattakeplace.

HavingreceivedtherequiredfilesfromtheWebserver,thebrowserthenrendersthepageontothescreenasspecifiedbyitsHTML,CSS,andotherWeblanguages.Anyimagesandotherresourcesareincorporatedtoproducetheon-screenWebpagethattheusersees.

MostWebpageswillthemselvescontainhyperlinkstootherrelatedpagesandperhapstodownloads,sourcedocuments,definitionsandotherWebresources.Suchacollectionofuseful,relatedresources,interconnectedviahypertextlinks,iswhatwasdubbeda"web"ofinformation.MakingitavailableontheInternetcreatedwhatTimBerners-LeefirstcalledtheWorldWideWeb（initsoriginalCamelCase,whichwassubsequentlydiscarded）inNovember1990.

Ajaxupdates

JavaScriptisascriptinglanguagethatwasinitiallydevelopedin1995byBrendanEich,thenofNetscape,forusewithinWebpages.ThestandardizedversionisECMAScript.Toovercomesomeofthelimitationsofthepage-by-pagemodeldescribedabove,somewebapplicationsalsouseAjax（asynchronousJavaScriptandXML）.JavaScriptisdeliveredwiththepagethatcanmakeadditionalHTTPrequeststotheserver,eitherinresponsetouseractionssuchasmouse-clicks,orbasedonlapsedtime.Theserver'sresponsesareusedtomodifythecurrentpageratherthancreatinganewpagewitheachresponse.Thustheserveronlyneedstoprovidelimited,incrementalinformation.SincemultipleAjaxrequestscanbehandledatthesametime,userscaninteractwithapageevenwhiledataisbeingretrieved.Somewebapplicationsregularlypolltheservertoaskifnewinformationisavailable.

WWWprefixinWebaddresses

ManyWebaddressesbeginwithwww,becauseofthelong-standingpracticeofnamingInternethosts（servers）accordingtotheservicestheyprovide.So,thehostnameforawebserverisoftenwwwasitisftpforanFTPserver,andnewsornntpforaUSENETnewsserveretc.ThesehostnamesthenappearasDNSsubdomainnames,asin"".

Theuseofsuchsubdomainnamesisnotrequiredbyanytechnicalorpolicystandard;indeed,thefirsteverwebserverwascalled"nxoc01.cern.ch",andmanywebsitesexistwithoutawwwsubdomainprefix,orwithsomeotherprefixsuchas"www2","secure"etc.Thesesubdomainprefixeshavenoconsequence;theyaresimplychosennames.Manywebserversaresetupsuchthatboththedomainbyitself（e.g.,）andthewwwsubdomain（e.g.,）refertothesamesite,othersrequireoneformortheother,ortheymaymaptodifferentwebsites.

Whenasinglewordistypedintotheaddressbarandthereturnkeyispressed,somewebbrowsersautomaticallytryadding"www."tothebeginningofitandpossibly".com",".org"and".net"attheend.Forexample,typing'microsoft'mayresolvetoand'openoffice'tohttp:

//www.openoffice.org.ThisfeaturewasbeginningtobeincludedinearlyversionsofMozillaFirefox（whenitstillhadtheworkingtitle'Firebird'）inearly2003.ItisreportedthatMicrosoftwasgrantedaUSpatentforthesameideain2008,butonlywithregardtomobiledevices.

The'http:

//'or'https:

//'partofwebaddressesdoeshavemeaning:

TheserefertoHypertextTransferProtocolandtoHTTPSecureandsodefinethecommunicationprotocolthatwillbeusedtorequestandreceivethepageandallitsimagesandotherresources.TheHTTPnetworkprotocolisfundamentaltothewaytheWorldWideWebworks,andtheencryptioninvolvedinHTTPSaddsanessentiallayerifconfidentialinformationsuchaspasswordsorbankdetailsaretobeexchangedoverthepublicinternet.Webbrowsersoftenprependthis'scheme'parttoURLstoo,ifitisomitted.Inoverview,RFC2396definedwebURLstohavethefollowingform:

:

//?

#.

Pronunciationof"www"

InEnglish,wwwispronouncedbyindividuallypronouncingthenameofcharacters（double-udouble-udouble-u）.Althoughsometechnicaluserspronounceitdub-dub-dubthisisnotwidespread.TheEnglishwriterDouglasAdamsoncequipped:

TheWorldWideWebistheonlythingIknowofwhoseshortenedformtakesthreetimeslongertosaythanwhatit'sshortfor.

–DouglasAdams,TheIndependentonSunday,1999

ItisalsointerestingthatinMandarinChinese,WorldWideWebiscommonlytranslatedviaaphono-semanticmatchingtowànwéiwǎng（万维网）,whichsatisfieswwwandliterallymeans"myriaddimensionalnet",atranslationthatveryappropriatelyreflectsthedesignconceptandproliferationoftheWorldWideWeb.

TimBerners-Lee'sweb-spacestatesthatWorldWideWebisofficiallyspelledasthreeseparatewords,eachcapitalized,withnointerveninghyphens.Additionally,Web（withacapitalW）isusedtoindicateitsstatusasanabbreviation.

Standards

ManyformalstandardsandothertechnicalspecificationsdefinetheoperationofdifferentaspectsoftheWorldWideWeb,theInternet,andcomputerinformationexchange.ManyofthedocumentsaretheworkoftheWorldWideWebConsortium（W3C）,headedbyBerners-Lee,butsomeareproducedbytheInternetEngineeringTaskForce（IETF）andotherorganizations.

Usually,whenWebstandardsarediscussed,thefollowingpublicationsareseenasfoundational:

∙Recommendationsformarkuplanguages,especiallyHTMLandXHTML,fromtheW3C.Thesedefinethestructureandinterpretationofhypertextdocuments.

∙Recommendationsforstylesheets,especiallyCSS,fromtheW3C.

∙StandardsforECMAScript（usuallyintheformofJavaScript）,fromEcmaInternational.

∙RecommendationsfortheDocumentObjectModel,fromW3C.

AdditionalpublicationsprovidedefinitionsofotheressentialtechnologiesfortheWorldWideWeb,including,butnotlimitedto,thefollowing:

∙UniformResourceIdentifier（URI）,whichisauniversalsystemforreferencingresourcesontheInternet,suchashypertextdocumentsandimages.URIs,oftencalledURLs,aredefinedbytheIETF'sRFC3986/STD66:

UniformResourceIdentifier（URI）:

GenericSyntax,aswellasitspredecessorsandnumerousURIscheme-definingRFCs;

∙HyperTextTransferProtocol（HTTP）,especiallyasdefinedbyRFC2616:

HTTP/1.1andRFC2617:

HTTPAuthentication,whichspecifyhowthebrowserandserverauthenticateeachother.

Privacy

Computerusers,whosavetimeandmoney,andwhogainconveniencesandentertainment,mayormaynothavesurrenderedtherighttoprivacyinexchangeforusinganumberoftechnologiesincludingtheWeb.Worldwide,morethanahalfbillionpeoplehaveusedasocialnetworkservice,andofAmericanswhogrewupwiththeWeb,halfcreatedanonlineprofileandarepartofagenerationalshiftthatcouldbechangingnorms.FacebookprogressedfromU.S.collegestu